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140

1 Cutting Action.

angle of relief or clearance angle, to keep the tool clear of the
work; A. the tutting angle, and c the tool angfe.

The point c requires great strength for metal tooling, and as
this makes A. very large, 'paring* cannot occur, but the material
will be 'crippled,' either by compression, shear, or a combination
of both. Sections parallel to F G will be in compression, and
those parallel to E G in shear, and it will be evident that along

of tool/

trv

some section E F, the material will "be weakened to the greatest
extent ; here then the shaving breaks so ranch as to curve up the
face of the tool The direction of E r will depend on- the relative
values of the compression and shear strengths of the material,

Great heat is generated, due to  molecular resistance and

friction.    A lubricant of soap and water** is  used for ductile

materials like wrought iron, contained in a can placed above the

tooi-tox, and led to the topi point by a wire, down which it

* Or soda, if rusting is to be avoided.